1. Field of the Invention
The present invention relates to a receiver and, more particularly, to a receiver for receiving a satellite broadcast (BS or CS broadcast), processing a received signal, converting the received signal to a CATV (cable television) signal, and outputting the CATV signal.
2. Related Art
Generally, a cable television system is constructed by CATV broadcast facilities disposed in the center and a number of CATV broadcast contracted receivers connected to the CATV broadcast facilities via RF transmission paths such as optical fibers or coaxial transmission paths. The CATV broadcast facilities provide various CATV broadcasts of a plurality of channels to each of the CATV broadcast contracted receivers via the RF transmission paths. On the other hand, the user of the contracted receiver selects a broadcast of a desired channel among the CATV broadcasts of the plurality of channels supplied from the CATV broadcast facilities and watches the selected broadcast by his/her contracted receiver.
The CATV broadcast facilities provide service of outputting a received satellite broadcast as a CATV broadcast to the RF transmission path. The service is received by an receiver comprising: a satellite broadcast tuner for receiving a satellite broadcast: a demodulating unit for demodulating an output signal of the satellite broadcast tuner and reproducing a baseband signal; a control unit for processing the demodulated baseband signal; a modulating unit for modulating the processed baseband signal and generating a modulated signal; and a CATV signal converting unit for converting the modulated signal into a CATV broadcast signal adapted to a CATV broadcast transmitted.
FIG. 4 is a block diagram showing an example of the configuration of a satellite broadcast signalxe2x80x94CATV broadcast signal converting mechanism, that is, a satellite broadcast receiver in known CATV broadcast facilities.
As shown in FIG. 4, the satellite broadcast receiver comprises: a BS broadcast receiving antenna 41; a satellite broadcast tuner 42 which is a BS tuner; an IC (Integrated Circuit) 43 for demodulation including an I/Q demodulating unit 431 and a QPSK demodulating unit 432; a control unit 44 for performing an MPEG process; an IC (Integrated Circuit) 45 for modulation including a QAM unit 451; a CATV signal converting unit 46; a digital-to-analog (D/A) converter 47; and a CATV signal output terminal 48.
The signal input terminal of the satellite broadcast tuner 42 is connected to the BS broadcast receiving antenna 41 and the signal output terminal is connected to the signal input terminal of the I/Q demodulating unit 431 The signal input terminal of the QPSK demodulating unit 432 is connected to the signal output terminal of the I/Q demodulating unit 431, and the signal output terminal of the QPSK demodulating unit 432 is connected to the signal input terminal of the control unit 44. The signal input terminal of the QAM unit 451 is connected to the signal output terminal of the control unit 44, and the signal output terminal of the QAM unit 451 is connected to the signal input terminal of the CATV signal converting unit 46. The signal output terminal of the CATV signal converting unit 46 is connected to the CATV signal output terminal 48. The signal input and output terminals of the digital-to-analog converter 47 are connected to the control signal output terminal of the control unit 44 and a channel selection signal input terminal of the satellite broadcast tuner 42 via an I square C (I2C) bus 49, respectively. An I2C bus 50 is connected between the control signal output terminal of the control unit 44 and the channel control terminal of the CATV signal converting unit 46 via the QAM unit 451 (IC 45 for modulation).
The satellite broadcast receiver having the above configuration operates as follows.
When a BS broadcast is received by the BS broadcast receiving antenna 41, the received signal is amplified and frequency-converted (down-converted) by the satellite broadcast tuner 42 and is outputted as an intermediate frequency signal. The intermediate frequency signal is converted by the I/Q demodulating unit 431 into an I signal and a Q signal whose phases are different from each other by 90 degrees. The I and Q signals are converted to QPSK modulated signals by the QPSK demodulating unit 432. The QPSK modulated signals are subjected to image compression by an MPEG process in the control unit 44 and the resultant signals are outputted as baseband signals. The baseband signals are subjected to quadrature amplitude modulation by the QAM unit 451. A quadrature amplitude modulated signal is amplified and frequency-converted (up-converted) by the CATV signal converting unit 46 and a resultant signal is outputted as a radio-frequency (RF) CATV signal to an RF transmission path (not shown) via the CATV signal output terminal 48.
In this case, a digital channel selection signal outputted from the control signal output terminal of the control unit 44 is supplied to the digital-to-analog converter 47 via the I2C bus 49 and is converted by the digital-to-analog converter 47 to an analog channel selection signal. The analog channel selection signal is supplied to a channel selection signal input terminal via the I2C bus 49 and the channel selection of the satellite broadcast tuner 42 is performed. A channel selection signal outputted from the control signal output terminal of the control unit 44 to the I2C bus 50 is supplied to the channel control terminal of the CATV signal converting unit 46 via the QAM unit 451 to select the channel of an RF signal outputted from the CATV signal converting unit 46.
In the known satellite broadcast receiver, the control unit 44, digital-to-analog converter 47, and satellite broadcast tuner 42 are connected via the I2C bus 49. Another known satellite broadcast receiver has a configuration such that the control unit 44, IC 43 for demodulation, and satellite broadcast tuner 42 are connected via the I2C bus.
The known satellite broadcast receiver has the configuration such that the control unit 44, digital-to-analog converting unit 47, and satellite broadcast tuner 42 are connected to the I2C bus 49 for transmitting a channel selection signal from the control unit 44 to the satellite broadcast tuner 42 or the configuration such that the control unit 44, IC 43 for demodulation, and satellite broadcast tuner 42 are connected to the I2C bus 49. Consequently, when a serial clock (SCL) and serial data (SDA) is transmitted via the I2C bus between the control unit 44 and the digital-to-analog converting unit 47 or between the control unit 44 and the IC 43 for demodulation, the serial clock and serial data is transmitted also to the satellite broadcast tuner 42 via the I2C bus. When the serial clock and serial data is supplied to the channel selection signal input terminal of the satellite broadcast tuner 42, digital frequency components of the serial clock and serial data are multiplexed on a local oscillation signal and supplied to the signal line. It increases pseudo noise (PN) components in a signal outputted from the satellite broadcast tuner 42, deteriorates the picture quality of a video signal in the signal, and reduces the carrier-to-noise ratio of the satellite broadcast tuner 42.
Similarly, the known satellite broadcast receiver has the construction in which the control unit 44, IC 45 for modulation and CATV signal converting unit 46 are connected. Consequently, when the serial clock (SCL) and serial data (SDA) is transmitted between the control unit 44 and the IC 45 for modulation, the serial clock and serial data is transmitted also to the CATV signal converting unit 46 via the I2C bus 50. In this case as well, when the serial clock and serial data is supplied to the CATV signal converting unit 46, the serial clock and serial data is multiplexed on signals from the parts in the CATV signal converting unit 46. It deteriorates the quality of the CATV signal outputted from the CATV signal converting unit 46.
The present invention has been achieved in consideration of the technical background. A first object of the invention is to provide a receiver which checks supply of unnecessary signal components by connecting a gate circuit to an I2C bus connected to a satellite broadcast tuner and turning on the gate circuit only when a channel selection signal is supplied to the satellite broadcast tuner.
A second object of the invention is to provide a receiver which checks supply of unnecessary signal components by connecting a gate circuit to an I2C bus connected to a CATV signal converting unit and turning on the gate circuit only when a channel selection signal is supplied to the CATV signal converting unit.
In order to achieve the first object, there is provided a receiver at least comprising: a satellite broadcast tuner; a demodulating unit; a control unit; a modulating unit; a CATV signal converting unit; and a digital-to-analog converting unit. The control unit, a unit controlled by a control signal from the control unit, and the satellite broadcast tuner are connected to each other via an I2C bus, and a channel selection signal outputted from the control unit is supplied to the satellite broadcast tuner via the I2C bus. The receiver has first means in which a gate circuit is connected to the I2C bus, a gate ON signal is supplied to the gate circuit only when the channel selection signal is supplied to the satellite broadcast tuner, and the channel selection signal is supplied to the satellite broadcast tuner via the gate circuit.
In an example of the first means, the controlled unit is an analog-to-digital converting unit connected between the control unit and the satellite broadcast tuner, the gate circuit is connected to the I2C bus which is provided between the analog-to-digital converting unit and the satellite broadcast tuner, and the gate ON signal outputted from the analog-to-digital converting unit is supplied to the gate circuit.
In another example of the first means, the controlled unit is an IC for demodulation including the demodulating unit, and the gate circuit is connected to the I2C bus provided between the IC for demodulation and the satellite broadcast tuner, and a gate ON signal outputted from the control unit is supplied to the gate circuit.
In order to achieve the second object, there is provided a receiver according to the invention at least comprising: a satellite broadcast tuner; a demodulating unit; a control unit; a modulating unit; a CATV signal converting unit; and a digital-to-analog converting unit. The control unit, an IC for modulation including the modulating unit, and the CATV signal converting unit are connected via an I2C bus for control signal transfer, and a channel selection signal outputted from the control unit is supplied to the CATV signal converting unit via the I2C bus. The receiver has second means in which a gate circuit is connected to the I2C bus positioned between the IC for modulation and the CATV signal converting unit, a gate ON signal is supplied from the control unit to the gate circuit only when the channel selection signal is supplied to the CATV signal converting unit, and the channel selection signal is supplied to the CATV signal converting unit via the gate circuit.
According to the first means, when the channel selection signal is supplied to the satellite broadcast tuner, the gate circuit connected to the I2C bus is opened and the channel selection signal is supplied to the satellite broadcast tuner via the opened gate circuit. On the other hand, when the channel selection signal is not supplied to the satellite broadcast tuner, the gate circuit is closed and no signal or no data is supplied via the I2C bus to the satellite broadcast tuner. Consequently, unnecessary signal and data components are not multiplexed on each of the parts of the satellite broadcast tuner. A good quality intermediate frequency signal can be therefore outputted from the satellite broadcast tuner and the operating state of the satellite broadcast tuner does not deteriorate.
According to the second means, when the channel selection signal is supplied to the CATV signal converting unit, the gate circuit connected to the I2C bus is opened and the channel selection signal is supplied via the opened gate circuit to the CATV signal converting unit. On the other hand, when the channel selection signal is not supplied to the CATV signal converting unit, the gate circuit is closed and no signal or no data is supplied to the CATV signal converting unit via the I2C bus, and unnecessary signals and data components are not multiplexed on parts of the CATV signal converting unit. Agood quality CATV signal can be outputted from the CATV signal converting unit and the operating state of the CATV signal converting unit does not deteriorate.